This invention generally relates to systems and procedures for developing work schedules. More specifically, the invention relates to systems and procedures for developing schedules for the steel manufacturing industry.
Usually, in a steel mill, a planning system defines what orders are to be produced next in a given plant. In a flat rolling steel mill, raw material is melted in pig iron that receives several alloys, which produces steel. Ladles of melted steel go through vacuum and purification processes until the final metallurgical specification is reached. Finally, the melted steel is poured into slabs. All of these steps happen in the Melt Shop (MS) Area. The next step in the process is the slab rolling operation in the Hot Strip Mill (HSM) Area. A slab can be rolled in several hot coil dimensions. Each of these two areas has its own constraints and objectives that are conflicting. For example: the MS wants to produce all the heats with the same cast grade in a row, which would produce a flat distribution of slabs regarding width. However, the HSM wants to roll slabs with a monotonic decreasing width sequence. Clearly, both are conflicting constraints.
Other areas of a steel mill present their own scheduling challenges. For example, the Finishing Area for a Steel Mill includes all the remaining production processes that start with hot coils and end with any finished product ready for shipping. The most important characteristic of the Finishing Area from the scheduling point of view is that the processing units are not tightly coupled. This means that a metallic unit (i.e., coil, blanket, sheet, . . . ) can wait for an indefinite period of time before going to the next processing unit. Another important feature about the Finishing Area is that each processing unit has its own set of constraints and rules to sequencing the metallic units for processing.
In addition, the Melt Shop area usually produces slabs that are rolled by the Hot Strip Mill (HSM) area, producing hot coils. A HSM area can include grinders, furnaces, and mills. Each slab has its own route through the HSM area, depending upon its cast grade, current dimensions, hot coil dimensions and order specifications.
An object of this invention is to improve scheduling procedures for steel mills.
Another object of the present invention is to provide a procedure for scheduling small sets of orders with similar characteristics, called heats, in a steel mill.
A further object of this invention is to provide an efficient solution for the finishing area scheduling problem for the steel industry.
Still another object of this invention is to provide an improved hot strip mill scheduling procedure.
A further object of the present invention is to provide a solution that interactively takes into consideration the melt shop (MS) area and the hot strip mill (HSM) area constraints such that a balanced and feasible solution is reached for the whole Primary Area (MS and HSM) at once.
These and other objectives are attained with the systems and procedures disclosed herein. In a first aspect, the present invention provides a unique algorithm that interactively takes into consideration the MS and the HSM constraints such that a balanced and feasible solution is reached for the whole Primary Area (MS and HSM) at once. In a second aspect, the invention takes a set of orders defined to be produced next in the Melt Shop area in a steel mill and groups them in small sets of orders with similar characteristics, called heats. Each order belongs to a heat. Each heat has a route that describes the production steps (processing units) that the heat has to go through in the Melt Shop. The system defines the precise moment that each heat has to be processed in each of its steps. Also, preferably the system considers restrictions such as temporal restrictions, raw material availability and ladle contamination. As output, the system provides the schedule of each processing unit and the instant that the slabs and ingots are created at the continuous casters.
In another aspect, the invention uses an event-driven based algorithm as a general approach for scheduling all the processing units with their specific constraints and the metallic units from hot coils to the finished products at the shipping areas. The system considers not only the material available at the execution moment, but also the material that will become available for every processing unit as time goes by. With a further aspect, the present invention provides a system that considers various constraints and assigns a precise start and finish time for each slab to be processed in each processing unit specified in the slab route. As its primary output, the system provides the exact moment the hot coils become available for the finishing area. The system provides a full set of intervention functions in the case that the user wants to adjust any aspect of the solution.